1. Field of the Invention
This invention relates generally to evaporative coolers and more specifically to an evaporative cooler air conditioning system; wherein an ambient airstream is cooled, sensibly, by means of a counter-flow heat exchanger such that evaporation continues within the heat exchanger in an exhausting airstream during the heat exchange process so that the temperature of the cooled air can be well below the wet-bulb temperature and even to a temperature close to the dew point temperature of the ambient air.
2. Description of the Prior Art
The concept of using evaporative cooler systems to provide an efficient method of cooling air for the purpose of cooling homes, apartments, industrial buildings, commercial buildings, house trailers and other enclosures, is old and well-established in the art.
In the past, there have been disclosed in the prior art many different apparatus and methods of using the cooling effect of the evaporation of water to lower the temperature of an airstream. Conventional evaporative coolers, cool air at a constant enthalpy; that is, the air is cooled by the evaporation of water without the addition or subtraction of heat. As a result, the minimum theoretical temperature which could be reached or to which a conventional evaporative cooler can cool the incoming air, is the wet-bulb temperature of its initial state.
In U.S. Pat. No. 1,985,529, to Ray; a process was disclosed whereby the temperature of the air circulated in an evaporate cooler air conditioning system was reduced below the wet-bulb temperature of the air entering the apparatus. In accordance with Ray's invention, raw or atmospheric air was introduced into a heat exchanger. The air emerged from the heat exchanger and entered a first vestibule, at which point, part of the air, having a lower dry and wet-bulb temperature than it did upon entering the heat exchanger, can be drawn off or bled for cooling purposes. The remaining air leaving the first vestibule entered a washer or humidifier where the air had a tendency to further cool the water. Since the air was not saturated, the air could absorb water, and continue to abstract heat from the air by conventional water vaporization.
The air left the washer and entered a second vestibule where part of it could be bled off for use, if desired. The air in the second vestibule was more saturated and lower in temperature than the air in the first vestibule. If the air in the second vestibule was bled off, it was required to place eliminators between the washer and point of bleeding to remove the entrained moisture. The saturated and cold air leaving the vestibule, and not bled off for use, was again washed with a spray of water to insure a high degree of saturation. It was then forced through the heat exchanger where the heat for the evaporation process could be drawn from the entering warm air.
Whereas this invention was capable of cooling air to below the wet-bulb temperature of the raw air or atmospheric air entering the heat exchanger, it was quite complicated, complex, required extensive spraying apparatus and ductwork and was quite expensive and relatively inefficient. Also, the cooled air was usually very high in humidity since it was exposed directly to the water in the wash compartment. The thermal efficiency of this system was, therefore, not nearly as high as it should have been or could have been.
U.S. Pat. No. 2,174,060, to Niehart, discloses an improved air conditioning apparatus that provided a means and operated by a method which comprised reducing the temperature of incoming air towards its dew point temperature by employing a heat transfer through a partition which was dry on one side and wet on the other. The total initial volume of the incoming air was first passed over the dry surface, and then was divided into a stream which flowed into the room to be cooled. A second stream which was then passed into contact with the wet side of the partition so that the air that contacted the wet side of the partition had already been reduced in temperature by its movement from the dry side. When the air first came into contact with the wet surface, this surface was at or near the new wet-bulb temperature and by the action of the heat transmitted through the partition from the dry side and taken up by water and air current, the wet-bulb temperature of the air flowing over the wet side increased until it had absorbed the heat being transmitted through the partition. Accordingly, more heat was absorbed through the process of increasing the wet-bulb temperature on the wet side of the partition and little heat was lost by increasing the temperature of the water therein.
The apparatus disclosed by Niehart incorporated the return of cold air into the hot end of the heat exchanger thereby resulting in the injection of cold air into a hot ambient airstream. This caused a lowering of the temperature at the hot end of the heat exchanger and a consequential lowering of the temperature of the humid exhaust air. Unnecessary heat was gained by the system due to a cooler exhaust air than need be. In addition, the cooling capacity of this system was greatly reduced to a lower amount of water per unit of mass flow of air that could be absorbed by the cold air entering the atmosphere of the wet evaporating chamber.
U.S. Pat. No. 4,023,949, issued on May 17, 1977 to Leslie A. Schlom et al for an EVAPORATIVE REFRIGERATION SYSTEM. This patent disclosed a system wherein air is evaporatively cooled by water in which the evaporating water is kept separate from the useful air of the cooled airstream by means of a heat exchanger so that cooling is performed without the addition of water vapor to the useful air and in which the working air absorbing the water vapor is drawn from the load. A heat exchanger is disclosed which operates by movement of the working air internally through tubular conduits concurrently to water flowing downward on the inner surfaces thereof while the air to be cooled passes externally across the conduits.
Therefore, the incoming fresh air is in an air-to-air cross-flow heat exchanger configuration to the return air and the return air is in an air-to-water counter-flow heat exchange configuration in which the water flows in the opposite direction. The Schlom et al application teaches a heat exchanger with separate dry sides and wet sides with the evaporating water being kept separate from the useful air so that cooling is performed without the addition of water vapor to the useful air; and all of the working air is drawn from the load and recirculated from the enclosure to be cooled to the wet side of the heat exchanger. Schlom et al specifically states that the wet side of the heat exchanger operates by movement of the working air internally through conduits counter-currently or in a counter flow with the water flowing downwardly along the conduit tubes inner surfaces while the useful air passes through the dry side in cross-flow to the return air in the conduit. This patent specifically teaches that the obtained increases in efficiency are due to flowing the moisture-laden return air exhausted from the wet side of the heat exchanger in a cross-flow heat exchanger which includes a separated relationship between the fresh air flow upstream from the dry side of the heat exchanger. Since the evaporating water is kept totally separate from the cooling airstream by means of the heat exchanger so the cooling is performed without the addition of water vapor, sensible cooling is achieved. While this patent represents an increase in efficiency, it nonetheless discloses a relatively complex and complicated system requiring costly equipment which still does not maximize the efficiency possible or solve many of the basic problems in evaporative cooler systems.
U.S. Pat. No. 4,188,994, issued to Louis W. Hinshaw on Feb. 19, 1980 for a COOLING AND HEATING APPARATUS. The patent teaches a cooling apparatus having an evaporative cooler interfaced with insulated air chamber and detachable therefrom to be replaced with a solar heater collecting panel. The insulated air chamber is connected to a home or other structure by a passage means; and the evaporative cooler is operable by other than the conventional electrical energy source as well as the usual electrical energy source so that the assembly can be used for cooling and heating of houses and other structures.
Hinshaw claims to be the first to use a dry air interface to directly cool air in an evaporative cooler system. The system involves exhausting the evaporated moisture into the atmosphere rather than into the building to be cooled. A metal plate is disposed on one face of the evaporative cooler to serve as an interface between the evaporative cooler and the body of the insulative box and the solar panel portion has been detached. As the warm air flows into the system and its temperature drops, moisture will condense and run off of the baffles and back on the interface into the bottom of the chamber. This will cause the cooling system to de-humidify the air as well as to cool it.
The heat exchange method of this patent is relatively expensive an ineffective and the efficiency of this system is far from that of the present evaporative system.
Therefore, a long-felt need has existed and continues to exist for an improved evaporative cooler system capable of efficiently cooling air below the wet-bulb temperature of the supply air while remaining relatively simple in design, structure, fabrication techniques required, and energy used.